Various procedures have previously been proposed for electrochemically removing dissolved or suspended material from aqueous solutions or suspensions thereof. Some of these prior procedures have involved the use of so-called "extended" electrodes where the aqueous electrolyte to be treated is passed through a relatively dense, essentially static bed of conductive particles positioned between a pair of electrodes. In an alternative approach, conductive particles are gently "fluidized" or suspended in the electrolyte as current is passed between the electrodes. In either case, the particles effectively extend the surface area of the electrodes and thus improve overall conductivity and heat transfer. Representative of these prior procedures are those described in the following U.S. Pat. Nos.:
3,728,238 PA1 3,730,864 PA1 3,755,114 PA1 3,764,498 PA1 3,915,822 PA1 3,919,062 While electrochemical procedures using extended electrodes of the type indicated may make it possible to remove various materials or contaminants from aqueous electrolytes for the purpose of improving the quality of the electrolyte and/or for recovery of the materials therein, certain disadvantages are also encountered. For example, undesired depositions tend to occur on the electrodes and the particles. This requires frequent cleaning and/or replacement of the electrodes and particles and reduces the cell efficiency. Undesired depositions are particularly likely to occur in the case where organic compounds present in the electrolyte are oxidized. This results in a gradual passivation of the electrode, usually the anode, and the creation of a high voltage drop at the electrode interface. Another problem is that complex organic compounds are not usually completely oxidized and there is a tendency to form by-products which give the treated electrolyte an undesirable yellow or brownish color. The deposition of residues on the anode and the discoloration of the electrolyte are particularly noticeable when the anode is immersed in a packed bed of electrically conductive particles. For example, with a packed bed of graphite particles, unacceptable fouling of the anode and discoloration of the electrolyte often occur even with low electric currents and low electrolyte temperatures. PA1 (1) The high degree of turbulence in the electrolyte insures faster reaction times and savings in power. More effective oxidation and/or reduction reactions can take place and suspended particulate contaminants can be readily agglomerated. Odor and colors can be removed from waste waters, and colloidal organics may be effectively oxidized, reduced and/or otherwise altered into an agglomerated state permitting easy mechanical removal. Compounds such as hydrogen sulfide, ammonium hydroxide, polychlorinated biphenols, organic pigments and the variety of organics occurring in conventional sewage can be oxidized and removed from the water regardless of the concentration involved.
High operating cost is another problem with prior procedures. Addtionally, they are often limited to the use of special conditions, e.g. narrowly controlled electrolyte pH and temperature and they normally are only effective using D.C. current.